Heat exchanger for pre-heating fluids



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. HEAT EXGHANGER FOR PRE-HEATING FLUIDS Filed Jan. 2. 1963 5 Sheets-Sheet 5 To ELEMENTS 0R MOTOR United States Patent O "ice 3,265,857 HEAT EXCHANGER FOR PRE-HEATING FLUIDS Gordon L. Benjamin, Jr., Barrington, RJ., assigner to Warren Electric Corporation, Warren, Rl., a corporation of Rhode Island Filed `Ian. 2, 1963, Ser. No. 249,049

7 Claims. (Cl. 219-331) The present invention relates to heat exchangers for use in the pre-heating ofV fluids.

In industrial heating'systems, lfor example, the grades of fuel oils used make their pre-heating desirable, particularly where the tank is so located as to be subject to low temperatures. Such pre-heating heat exchangers include heating means for the oil and Acircuitry therefor that is opened when the oil temperature is at or above a suit- -able temperature and closed when .the oil temperature drops.

Several requirements for such heat exchangers exist for this and other uses and among these may be noted the requirement that they must provide `an adjustable basis for maintaining the temperature of the oil or other fluid in a desired temperature range over a wide range of operating conditions and, particularly, that they must maintain the cycle curve relatively flat to ensure maximum efficiency and economy.

In accordance with the invention, these general objectives are attained by providing a heat exchanger having electric heating means for entry into the fluid, the circuitry for which includes switch means which are preferably normally open. A unit responsive to the temperature of the fluid has a sensing part in the fluid anda shaft which moves axially in response to temperature variations of the fluid. A switch operating lever is actuated by the shaft on an increase in temperature and .it controls the switch means to then open the circuitry to the heating means. Means are provided to oppose such movement until the Huid is at a Ipredetermined. elevated temperature.

In the operation of a heat exchanger in pre-heating fluids, the temperature ofthe lluid rises until the switch means opens in response to the actuation of the temperature responsive unit. The temperature continues to -rise for an .interval and then starts to drop. Because of various factors, such as switch characteristics and the mechanism actuated by the temperature responsive unit, the switch means does not close until the temperature drops below that temperature at which the switch means opens and, of course, the temperature continues to drop Afor an interval even after the circuitry to the heating means is closed. It is desirable that the temperature curves representing the operating cycle be .as llat 4as possible and, for this reason, the lever affords such mechanical advantages that an adequate `stroke is provided to ensure switch operation on substantially smaller temperature changes than has hitherto been possible. In one embodiment of the invention, the heating means is in the form of two sets of heating elements with each set being in a circuit separate from the other and including its own switch. While the Vtwo switches may be operated at dierent temperatures, one after the other, it is preferred that both switches be operated simultaneously by a single lever having substantial mechanical advantage thus ensuring positive control of the switches on Ia small variation in temperature.

A reason for providing two sets of heating elements, each set in its own circuit and provided with its own switch, is that the combined load of the two sets is greater than that for which a single switch of the desired type is presently available. r1`he heating elements may, however, all be included in a single circuit, if controlled by a relay in a circuit having a lever-controlled switch. A similar circuit may also be utilized for the operation of a motor 3,265,857 Patented August 9, 1966 switch, for example, as is used for the fluid delivery pump.

Smooth and reliable operation is important to the uniform attainment of switch control on small temperature changes and an objective of the invention is to minimize Afriction between a thrust member carried by the shaft and the lever engaged thereby 'and this result is attained by providing rotatable members between the thrust member that provide a rolling thrust surface as the lever is pivoted.

Another objective is to have the switch means arranged with the operating element or elements movable transversely and to use levers in the form of bell cranks.

In the accompanying drawings, there are shown illustrative embodiments of the invention from which these and other of its objectives, novel features, and advantages will be readily apparent, the embodiments being particularly for use in the pre-heating of fuel oil.

In the drawings: g

FIGURE l is a schematic view of a typical oil burner installation of the type requiring that the oil be preheated,

FIGURE 2 is a view of typical circuitry for a heatv exchanger for use in such oil pre-heating,

FIGURE 3 is a view, taken `from thek contr-ol Vend of .a heat exchanger in accordance with the invention, the coverv having been removed,

, FIGURE 4 is a longitudinal section of the heat exchanger with the cover` in place,

FIGURE 5 is a section taken approximately along the indicated lines 5 5 of FIGURE 4, Y'

FIGURE 6 is a section taken approximately along the indicated lines 6 6 of FIGURE 3,

FIGURE 7 is a section taken approximately along the indicated lines 7-7 of FIGURE 6,

FIGURE 8 is a fragmentary section showing the connection between the shaft and actuating lever as seen as if viewed at right angles to the showing of those parts in FIGURE 6, n

FIGURE 9 is a perspective View of the actuating lever controlling the heating circuit,

FIGURE l0 is an enlarged section taken approximately along the indicated lines 11B-lil of FIGURE 8,

FIGURE l1 is a section taken along the indicated lines 11-11 of FIGURE 10,

FIGURE 12 is a fragmentary and longitudinally sectioned View of the control end of another heat exchanger in accordance with the invention,

FIGURE 13 is a fragmentary end view of the heat exchanger shown in FIGURE l2,

FIGURE 14 is a side View thereof,

FIGURE l5 is a schematic view illustrating the circuitry used for three phase operation, and

FIGURE 16 is a view illustrating a typical cycle curve using an on-otf type of thermostat.

A typical industrial oil burner installation, as schematically represented in FIGURE l, has an outside storage tank 2t) with a supply circuit 21 provided with a pump 22 and connected to the oil burner 23. Because the temperature of the oil in the tank 20 is often too low for eicient combustion, it is a common practice to place a heat exchanger in the conduit 21 with the heat exchanger having oil heating means and switch controlling lmeans responsive to the temperature of the oil in the heat exchanger.

A heat exchanger in accordance with the invention is generally indicated at 24 and includes a flanged chamber 25 secured to a mount 26 through which extend the ends of the heating elements which are shown as U-shaped and arranged as two sets. One set includes heating elements 27, 28, and 29 and the other set includes heating elements 30, 31, and 32. The elements of the set 30, 31, and 32 are sutliciently shorter than those of the set 27, 28, and

29 so that they may be located in the space dened thereby at right angles thereto. The heating elements are of a commonly used type consisting, as illustrated by element 32 in FIGURE 5, of a resistance wire 32A inside of and insulated from a metallic tube 32B by a refractorylike material 32C acting both as a heat conductor and an electrical insulator.

The elements of the set 27, 28, and 29 are in a lead 33 and the elements 30, 31, and 32 are in a parallel lead 34. The leads 33 and 34 include switches 35 and 36, respectively, and have a common ground 37, see FIGURES 2 and 3. As stated before, control switches for use in a heat exchanger for use as an oil pre-heater are of the snap-action type and because of Vthe load established by the six heating elements, the heating elements are arranged in two sets Vto provide loads within the limits for which presently available switches of the above indicated type are rated.

The switches 35 and 36 are normally open snap-action switches and have plungers 38 and 39, respectively, which, when depressed, establish the closed position of the switches 35 and 36. One such commercially available switch is obtainable with an operating differential of approximately .005 inch maximum. VThe switches 35 and 36 are mounted, side-by-side, in a chassis 40 having legs 41 attached to the mount 26.

In order that the switches 35 and 36 may be operated properly in response to the temperature of the oil, a sensing bulb 42'is attached to one or more of the heating elements, the elements 27 4and 32, for example, by spring clips 43 whose positions may be varied to ensure the desired contact of the bulb42 with the heating element or elements, see 'FIGURES 4 and 5, regardless of minor surface irregularities of the heating elements or of the sensing bulb 42. The bulb 42 is connected to a diaphragm 44 by a tube 45 and, together, they establish a conventional, hermetically-sealed unit filled with la uid having a constant rate of expansion. As the temperature of the sensing bulb 42 increases, the diaphragm 44 is expanded and raises its stern 46.

The stem 46 has an axial bore 46A which receives and holds centered an axial pin 47A on the lower end of the threaded shaft 47. A bushing 48 is a sliding fit in an axial bore` 49 in the end wall 50 of t-he chassis 40 Iand it has an axial bore 51 which is threaded to receive and hold centered the upper end of the shaft 47. A nut 52, threaded on the lower end of the shaft 47, is held against rotation by the lower fork 53A of .a retainer'53.

The shorter end 54A of a bell crank 54 is bored as at v55 to freely receive the shaft 47 and is attached to the chassis 40 by a pivot 56. The longer end 54B of the lever 54 is engageable with the switch plungers 38 and 39 with yadjustable screws 57 being provided for engagement with the plungers to ensure correct switch actuation, in t-he illustrated case, the simultaneous opening and closing of the switches 35 and 36. The `shorter end 54A has parallel grooves 58, see FIGURES `8-11, one groove for each of the balls 59 which `are loosely confined by holes 60A in a retainer 60 held in place by the shaft 47 which passes freely through the opening 66B and seated -against the upper surface of the -nut 52 which, with respect to the Ilever 54 is a thrust member.

From the foregoing, it will be apparent that as the temperature of the oil increases, the diaphragm and accordingly the shaft 47 is moved upwardly in -a switchopening direction. Such movement is opposed by a spring 61 surrounding the shaft 47 and backed by the short end 62A of a second bell crank 62, the end 62A being apertured to receive the shaft 47 freely and pivoted as at 63 to the chassis 40. The longer end 62B of the bell crank 62 engages the plunger 64 of a switch 65, preferably of a normally open, snap-action type and in a circuit 66 to the motor 67 by which the pump 22 is driven.

The surface of the bell crank end 62A has a pair of parallel grooves 68 for the balls 69 which are held seated against a plate 70 by a retainer 71 and as this arrangement is substantially identical to the anti-friction connection between the lever 53 and the nut 52, it is not separately illustrated. The plate 70 is backed by the threaded bushing 48 and is held against rotation by the upper fork 53B of the retainer 53. The retainer 53 is attached to the chassis 40 as by means of the bell crank pivots 56 and 63. A spring 72, .backed by the end wall 50 of the chassis 40 resiliently engages the plate 70.

It will be apparent that, by rotating the shaft 47, the position of the nut 52 and of the bushing 48 is varied and in practice, see FIGURE 3, the shaft 47 has an arm 73 movable with reference `to indicia 74, see FIGURE 3. When the shaft 47 is rotated in a clockwise direction, as viewed in FIGURE 3, the pin 47A is advanced into the seat 46A to require correspondingly shorter travel of the diaphragm actuated stern 46 so lthat the switches are opened at a lower temperature, vice versa, on rotation of the shaft 47 in the opposite direction. In practice, the spring 72 exerts a force that is great enough to establish a normal position of the bell cranks in which the normal switch positions prevail While the spring 61 holds the balls under a compression load while leaving them free to move in their respective grooves within the limits established by the associated retainers.

With reference to FIGURE 16, a typical heating cycle curve is shown and is representative of temperatures taken at the discharge from the exchanger or on the surface of the heating elements. Maximum and minimum temperatures are, in fact, greater on the elements. The heat exchanger isy adjusted to open and close the heating circuitry at a selected temperature represented by a point ori a curve, say the point A, but thetemperature of the oil in the chamber will continue to rise to a higher point, say the point B and because of various factors, such a switch characteristic and the characteristics of the switch operating mechanism, the switches do not close until the point C is reached although the temperature continues to drop to a lower point, say the point D.

Because `of the mechanical advantage afforded by the mechanism of heat exchangers in accordance with the invention and because of the reduction of friction, the

difference between points B and D can be substantially p reduced which has the important advantage of flattening the curve, an objective of any close tolerance thermostatic control, substantially to the limits A and C which .are minimized due to the above described features.

The embodiment of the invention illustrated by FIG-- URES 12-15 is herein discussed with particular reference to three phase operation. With reference to FIGURE 15, a three phase circuit 75 is shown as controlled by a generally indicated relay 76 energized when the switch 77 is closed, the switch 77 being in a low voltage, single phase circuit 78. The circuit 75 can be either a motor circuit or a heater circuit but in FIGURES 12-14, the motor circuit is not shown in order to simplify the drawing as well as to illustrate the construction when only the heater circuitry is controlled in response to variations in the temperatures of the oil.

In FIGURES 12-14, the construction, except for the three phase circuitry and the omission of the motor switch, is the same as that previously described. For this reason, it is not again detailed other than to note that the use of the relay 76 and the switch 77 for the circuit 75 enables a narrower chassis 40A to be used. The switch 77 is normally open and is shown as of the same type as the switches 35, 36, and 65 and is held closed, during oil heating, by the bell crank 79 which is similar to but narrower than the bell crank 54.

Assuming that the heater circuitry is not controlled by variations in the temperature of the oil, the chassis 40A carries only the switch 77 and this requires the use of a plate 70A which is backed by the spring 72 and which is recessed as at 70B to actuate the upper end of the spring 61. The operation of the device shown in FIGURES 12-14 is otherwise the same as that containing switches for two or more circuits.

From the foregoing, it will be appreciated that heat exchangers in accordance with the invention are well adapted for use in pre-heating fuel oil since they are readily adjustable to different conditions and are well adapted to function with a relatively flat cycle curve and with the temperature differential between the points when the heating circuitry is open and that when it is closed held to a minimum ensuring efllciency and economy.

il claim:

1. In a heat exchanger for use in pre-heating a fluid, a mount, electrical heating means supported by said mount for entry into said fluid, circuitry including said heating means and switch means supported by said mount, a temperature responsive unit carried by said mount and including a part for entry into said fluid and a shaft movable axially in response to variations in the temperature of the fluid, said shaft including a thrust portion, -a lever pivotally supported by said mount and including a portion overlying said thrust portion through which Y said shaft freely extends, said lever operatively engaging said switch means to effect the opening of said circuitry on `an increase in the temperature of the fluid, a spring backed by the 4portion of said shaft extending thnough said overlying lever portion and yieldably engaging therewith, and a plurality of rotatable members confined between said portio-ns and in contact therewith a-s said lever swings, and means confining said rotatable members in transversely alined, pivot-establishing relati-onship to said overlying portion of said lever.

2. In a heat exchanger for use in pre-heating a fluid, a mount, electrical heating means lsupported by said mount for entry into said fluid, circuitry including said heating means and switch means supported by said mount, a temperature responsive unit carried by said mount including a part for entry into said fluid and a shaft movable axially in response to variations in the temperature of the fluid and including a thrust portion, and a bell crank lever including arms of unequal length, the shorter arm overlying said shaft thrust portion and being pivotally supported by said mount and having a hole through which the shaft freely extends, a plurality of anti-friction members confined between said thrust portion and said shorter arm, and the end of the 'longer arm of said lever operatively engaging said yswitch means to effect the opening of said circuitry on an increase in the temperature of the fluid, a spring backed by the portion of said Shaft extending through said shorter arm and yieldably engaging therewith,-and means confining said anti-friction members in transversely alined, pivot-establishing relationship to -said yshorter arm.

3. In a heat exchanger for use in pre-heating a fluid, a mount, electrical heating means for entry into said fluid supported by said mount, circuitry including said heating means and switch means supported by said mount, a second circuit including switch means supported by Isaid mount, a temperature responsive unit including a part for entry into said fluid and including a shaft movable axially in response tio variations in the ternperature of the fluid, and levers pivotally supported by said mount, one lever for each switch means and operatively engaging that switch means on an increase in the temperature of the fluid, both of said levers being bell cranks each having a short arm and a long anni, -the short arms being located one above the other. and having a bore through which said shaft freely extends, the longer arms of each lever being disposed towards the shorter arm of the other, a spring interposed between said short arms, a thrust member carried by said shaft below the `lowermost short arm and engageable therewith on upward movement of said shaft, and means above the uppermost short lever arm resiliently engaging therewith.

4. The heat exchanger of claim 3 in which the thrust member is threaded on the shaft.

5. The` heat exchanger of claim 3 in which the means engaging the uppermost short lever arm includes a part threaded on the shaft.

5. In a heat exchanger Afor use in pre-heating a fluid, a mount, electrical heating means for entry intoy said fluid supported by said mount, circuitry including said heating means and switch means, a temperature responsive unit including a part for entry into said fluid and including a stem and a shaft, said stem and shaft having a connection enabling said shaft t-o be moved axially relative thereto while connected and to be detached therefrom by like movement in the appropriate direction, said stem and shaft being movable axially in response to variations in the temperature of the fluid, and a lever connected to said shaft to be moved thereby, said 'lever operatively engaging said switch means establishing the closed position thereof until moved by said shaft on an increase in the temperature of the fluid, said mount including a detachable chassis by which said switch means and said shaft are supported and to which said lever is pivoted.

7. In a heat exchanger for use "in pre-heating a fluid, a mount, electrical heating means for entry into said fluid supported iby said mount, circuitry including said heating means and switch means supported by said m-ount, a temperature responsive unit including a part for entry into said fluid and including a stem and a shaft movable axially in response to variations in the temperature of the fluid, said stem and said shaft having a connection enabling said -shaft to be moved relatively to said stem while connected, and a lever pivotally supported by said mount, a thrust member threaded on said shaft and englageable with said lever, and said lever operatively engaging said switch means establishing the closed position thereof until moved by said shaft on an increase in' the temperature of the fluid, adjustable means yieldably opposing movement of said shaft and lever and including a part threaded on said shaft, and common means holding said part and said thrust member against rotation.

References Cited by the Examiner UNITED STATES PATENTS 1,330,892 2/1920 Moloney 200-137 1,787,450 1/1931 Lonergan 219-331 X 2,039,641 5/ 1936 Fichtner 219-523 X 2,104,848 1/1938 Clark 219-321 X 2,210,526 8/1940 Burling 200-137 2,217,595 10/1940 Morgan et al 219-331 X 2,270,738 l/ 1942 Lightfoot 200-137 2,460,762 2/ 1949 Minnich 200-140 2,498,988 2/ 1950 Eden et al.

2,916,598 1'2/1959 Hayden 219-321 X 3,050,600 8/1962 Booth et a'l 200-140 X FOREIGN PATENTS 1,137,397 1/1957 France.

RICHARD M. WOOD, Examiner.

ANTHONY BARTIS, Acting Primary Examiner. 

3. IN A HEAT EXCHANGER FOR USE IN PRE-HEATING A FLUID, A MOUNT, ELECTRICAL HEATING MEANS FOR ENTRY INTO SAID FLUID SUPPORTED BY SAID MOUNT, CIRCUITRY INCLUDING SAID HEATING MEANS AND SWITCH MEANS SUPPORTED BY SAID MOUNT, A SECOND CIRCUIT INCLUDING SWITCH MEANS SUPPORTED BY SAID AMOUNT, A TEMPERATURE RESPONSIVE UNIT INCLUDING A PART FOR ENTRY INTO SAID FLUID AND INCLUDING A SHAFT MOVABLE AXIALLY IN RESPONSE TO VARIATIONS IN THE TEMPERATURE OF THE FLUID, AND LEVERS PIVOTALLY SUPPORTED BY SAID MOUNT, ONE LEVER FOR EACH SWITCH MEANS AND OPERATIVELY ENGAGING THAT SWITCH MEANS ON AN INCREASE IN THE TEMPERATURE OF THE FLUID, BOTH OF SAID LEVERS BEING BELL CRANKS EACH HAVING A SHORT ARM AND LONG ARM, THE SHORT ARMS BEING LOCATED ONE ABOVE THE OTHER AND HAVING A BORE THROUGH WHICH SAID SHAFT FREELY EXTENDS, THE SHORTER ARMS OF EACH LEVER BEING DISPOSED TOWARDS THE SHORTER ARMS OF THE OTHER, A SPRING INTERPOSED BETWEEN SAID SHORT ARMS, A THRUST MEMBER CARRIED BY SAID SHAFT BELOW THE LOWERMOST SHORT ARM AND ENGAGEABLE THEREWITH ON UPWARD MOVEMENT OF SAID SHAFT, AND MEANS ABOVE THE UPPERMOST SHORT LEVER ARM RESILIENTLY ENGAGING THEREWITH. 